Pattern formation methods and photoresist pattern overcoat compositions

ABSTRACT

A pattern formation method, comprising: (a) providing a semiconductor substrate; (b) forming a photoresist pattern over the semiconductor substrate, wherein the photoresist pattern is formed from a photoresist composition comprising: a first polymer comprising acid labile groups; and a photoacid generator; (c) coating a pattern overcoat composition over the photoresist pattern, wherein the pattern overcoat composition comprises a second polymer and an organic solvent, wherein the organic solvent comprises one or more ester solvents, wherein the ester solvent is of the formula R 1 —C(O)O—R 2 , wherein R 1  is a C3-C6 alkyl group and R 2  is a C5-C10 alkyl group; (d) baking the coated photoresist pattern; and (e) rinsing the coated photoresist pattern with a rinsing agent to remove the second polymer. The methods find particular applicability in the manufacture of semiconductor devices.

BACKGROUND

The invention relates generally to the manufacture of electronicdevices. More specifically, this invention relates to pattern formationmethods and to photoresist pattern overcoat compositions useful in theformation of fine lithographic patterns.

In the semiconductor manufacturing industry, photoresist materials areused for transferring an image to one or more underlying layers, such asmetal, semiconductor and dielectric layers, disposed on a semiconductorsubstrate, as well as to the substrate itself. To increase theintegration density of semiconductor devices and allow for the formationof structures having dimensions in the nanometer range, photoresists andphotolithography processing tools having high-resolution capabilitieshave been and continue to be developed.

Positive-tone chemically amplified photoresists are conventionally usedfor high-resolution processing. Such resists typically employ a resinhaving acid-labile leaving groups and a photoacid generator. Patternwiseexposure to activating radiation through a photomask causes the acidgenerator to form an acid which, during post-exposure baking, causescleavage of the acid-labile groups in exposed regions of the resin. Thiscreates a difference in solubility characteristics between exposed andunexposed regions of the resist in an aqueous alkaline developersolution. In a positive tone development (PTD) process, exposed regionsof the resist are soluble in the aqueous alkaline developer and areremoved from the substrate surface, whereas unexposed regions, which areinsoluble in the developer, remain after development to form a positiveimage.

Lithographic scaling has conventionally been achieved by increasing thenumerical aperture of the optical exposure equipment and using shorterexposure wavelengths. At present, ArF (193 nm) lithography is thestandard for mass production of advanced semiconductor devices. ArFphotoresist polymers are typically based on (meth)acrylate chemistry andare free or substantially free of aromatic groups in the polymer due totheir high absorption at the exposure wavelength. To form finerphotoresist patterns than attainable by direct imaging alone,photoresist pattern trimming processes have been proposed, for example,in US2014/0186772A1. Photoresist trimming processes typically involvecontacting a photoresist pattern that includes a polymer having acidlabile groups with a composition containing an acid or thermal acidgenerator. The acid or generated acid causes deprotection in a surfaceregion of the resist pattern, which region is then removed, for example,by contact with a developer solution. This allows for trimming of thephotoresist pattern, for example, resulting in the creation of finerresist line and pillar patterns, or larger diameter contact holepatterns, than when using direct imaging alone.

To form finer device geometries than possible with Arf lithography, EUV(e.g., 13.5 nm) lithography methods and materials have been and continueto be developed for next-generation semiconductor devices. An advantageof this technology is the lack of absorption of EUV radiation byaromatic groups, thereby opening up the possibility for use ofphotoresist material platforms not practical for ArF lithography, forexample, vinyl aromatic-based polymers such as polyhydroxystyrene(PHS)-based polymers. Such materials can be beneficial, for example,from the standpoint of one or more of etch resistance, etch selectivity,sensitivity and cost. The use of ArF resist pattern trimming productswith aromatic-based photoresist polymer systems, however, has been foundto result in poor patterning performance, for example, in local criticaldimension uniformity (LCDU), coating defects and pattern damage.

There is a need in the art for photoresist pattern formation methods andresist pattern overcoat compositions useful in electronic devicefabrication that address one or more problems associated with the stateof the art.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, pattern formationmethods are provided. The methods comprise: (a) providing asemiconductor substrate; (b) forming a photoresist pattern over thesemiconductor substrate, wherein the photoresist pattern is formed froma photoresist composition comprising: a first polymer comprising acidlabile groups; and a photoacid generator; (c) coating a pattern overcoatcomposition over the photoresist pattern, wherein the pattern overcoatcomposition comprises a second polymer and an organic solvent, whereinthe organic solvent comprises one or more ester solvents, wherein theester solvent is of the formula R₁—C(O)O—R₂, wherein R₁ is a C3-C6 alkylgroup and R₂ is a C5-C10 alkyl group; (d) baking the coated photoresistpattern; and (e) rinsing the coated photoresist pattern with a rinsingagent to remove the second polymer.

Also provided are photoresist pattern overcoat compositions. Thecompositions comprise: a matrix polymer comprising a repeat unitcomprising a —C(CF₃)₂OH group and/or a repeat unit comprising an acidgroup; and an organic solvent comprising one or more ester solvents,wherein the ester solvent is of the formula R₁—C(O)O—R₂, wherein R₁ is aC3-C6 alkyl group and R₂ is a C5-C10 alkyl group.

Also provided are coated substrates. The coated substrates comprising: asemiconductor substrate; a photoresist pattern over the substrate; and aphotoresist pattern overcoat composition as described herein over and incontact with the photoresist pattern.

Preferable methods and compositions of the invention can providephotoresist patterns having improved characteristics, for example, inone or more of local CD uniformity (LCDU), coating defectivity andresist dimension reduction.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention.The singular forms “a”, “an” and “the” are intended to include singularand plural forms, unless the context indicates otherwise.

DESCRIPTION OF THE DRAWINGS

The present invention will be described with reference to the followingdrawing, in which like reference numerals denote like features, and inwhich:

FIG. 1A-H illustrates an exemplary process flow for forming aphotolithographic pattern in accordance with the invention.

DETAILED DESCRIPTION Photoresist Pattern Overcoat Compositions

Photoresist pattern overcoat compositions of the invention include apolymer and a solvent, and can include one or more optional additionalcomponents. The polymer allows for the compositions to be coated overthe photoresist pattern in the form of a layer having a desiredthickness. The polymer should have good solubility in the rinsing agentto be used in the patterning process. For example, the matrix polymercan be soluble in an aqueous alkaline solution such as those typicallyused as photoresist developers, preferably aqueous quaternary ammoniumhydroxide solutions such as aqueous tetramethylammonium hydroxide (TMAH)(e.g., a 0.26N TMAH solution). To minimize residue defects originatingfrom the pattern overcoat composition, the dissolution rate of a driedlayer of the overcoat composition in a rinsing agent to be appliedshould be greater than that of the photoresist pattern in the rinsingagent. The matrix polymer typically exhibits a dissolution rate in therinsing agent, preferably a 0.26N TMAH solution, of 100 Å/second orhigher, preferably 1000 Å/second or higher. The matrix polymer should besoluble in the solvent of the overcoat composition, described herein.

The matrix polymer can be formed from one or more monomers chosen, forexample, from those having an ethylenically unsaturated polymerizabledouble bond, such as: (meth)acrylate monomers such asisopropyl(meth)acrylate and n-butyl(meth)acrylate; (meth)acrylic acid;vinyl aromatic monomers such as styrene, hydroxystyrene andacenaphthylene; vinyl alcohol; vinyl chloride; vinyl pyrrolidone; vinylpyridine; vinyl amine; vinyl acetal; and combinations thereof.Preferably, the matrix polymer contains one or more functional groupschosen, for example, from hydroxyl, acid groups such as carboxyl,sulfonic acid and sulfonamide, silanol, fluoroalcohol such ashexafluoroisopropyl alcohol [—C(CF₃)₂OH], anhydrates, lactones, esters,ethers, allylamine, pyrrolidones and combinations thereof. Of these,—C(CF₃)₂OH and acid groups such as carboxyl, sulfonic acid andsulfonamide are particularly preferred. The matrix polymer can be ahomopolymer or a copolymer having a plurality of distinct repeat units,for example, two, three, four or more distinct repeat units. In oneaspect, the repeat units of the matrix polymer are all formed from(meth)acrylate monomers, are all formed from (vinyl)aromatic monomers orare all formed from (meth)acrylate monomers and (vinyl)aromaticmonomers. When the matrix polymer includes more than one type of repeatunit, it typically takes the form of a random copolymer. Suitable matrixpolymers in accordance with the invention include, for example, thefollowing:

wherein the unit contents are in mol %.

The content of the matrix polymer in the composition will depend, forexample, on the target thickness of the layer, with a higher polymercontent being used when thicker layer is desired. The matrix polymer istypically present in the pattern overcoat composition in an amount offrom 80 to 100 wt %, more typically from 90 to 100 wt %, 95 to 100 wt %,99 to 100 wt %, or 100 wt %, based on total solids of the overcoatcomposition. The weight average molecular weight (Mw) of the matrixpolymer is typically less than 400,000, preferably from 3000 to 50,000,more preferably from 3000 to 25,000, as measured by GPC versuspolystyrene standards. Typically, the matrix polymer will have apolydispersity index (PDI=Mw/Mn) of 3 or less, preferably 2 or less, asmeasured by GPC versus polystyrene standards.

The overcoat compositions typically include a single polymer, but canoptionally include one or more additional polymers. Suitable polymersand monomers for use in the overcoat compositions are commerciallyavailable and/or can readily be made by persons skilled in the art. Forexample, the matrix polymer may be synthesized by dissolving selectedmonomers corresponding to units of the polymer in an organic solvent,adding a radical polymerization initiator thereto, and effecting heatpolymerization to form the polymer. Examples of suitable organicsolvents that can be used for polymerization of the matrix polymerinclude, for example, toluene, benzene, tetrahydrofuran, diethyl etherand dioxane. Suitable polymerization initiators include, for example,2,2′-azobisisobutyronitrile (AIBN),2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl2,2-azobis(2-methylpropionate), benzoyl peroxide and lauroyl peroxide.

The overcoat compositions further include one or more solvents. Suitablesolvent materials to formulate and cast the overcoat compositionsexhibit very good solubility characteristics with respect to thenon-solvent components of the overcoat composition, but do notappreciably dissolve the underlying photoresist pattern so as tominimize intermixing. The overcoat compositions are preferably organicsolvent-based, meaning greater than 50 wt % organic solvents, and moretypically greater than 90 wt %, greater than 95 wt %, greater than 99 wt% or 100 wt % organic solvents, based on the total solvents of theovercoat compositions.

The solvent comprises one or more ester solvents of the formulaR₁—C(O)O—R₂, wherein R₁ is a C3-C6 alkyl group and R₂ is a C5-C10 alkylgroup. Preferred such ester solvents include, for example, isoamylisobutyrate, n-Pentyl isobutyrate, Isoamyl n-butyrate, n-Pentyln-pentanoate, Isoamyl isopentanoate, n-Hexyl isobutyrate, 2-Ethylhexylisobutyrate, Isoamyl valerate, Isoamyl 2-methylvalerate and combinationsof such ester solvents. Of these, Isoamyl isobutyrate is particularlypreferred. The use of such an ester solvent is believed to contribute toimproved LCDU as compared with an untreated resist pattern and lowerdefectivity than known resist pattern trimming compositions whentreating vinyl aromatic-based photoresist patterns. Without wishing tobe bound by any particular theory, it is believed that the polar natureof the ester solvent lends itself to these properties. The one or moreester solvent solvents of the above formula are typically present in acombined amount of from 1 to 100 wt %, preferably from 2 to 30 wt % orfrom 3 to 10 wt %, based on the total solvent of the overcoatcomposition.

The overcoat compositions may include one or more additional solventtypes. For example, the overcoat compositions preferably further includeone or more monoether solvents. If present in the compositions, the oneor more monoether solvents are typically present in a combined amount offrom 50 to 99 wt %, preferably 70 to 98 wt % or 90 to 97 wt %, based ontotal solvents of the overcoat composition. Use of a monoether-basedsolvent system can provide desirable (low) toploss characteristics whentreating vinyl aromatic-based photoresist patterns.

Preferred monoether solvents include alkyl monoethers and aromaticmonoethers, particularly preferred of which are those having a totalcarbon number of from 6 to 16. Suitable alkyl monoethers include, forexample, 1,4-cineole, 1,8-cineole, pinene oxide, di-n-propyl ether,diisopropyl ether, di-n-butyl ether, di-n-pentyl ether, diisoamyl ether,dihexyl ether, diheptyl ether and dioctyl ether, with diisoamyl etherbeing preferred. Suitable aromatic monoethers include, for example,anisole, ethylbenzyl ether, diphenyl ether, dibenzyl ether andphenetole, with anisole being preferred.

Other suitable solvents for the overcoat compositions include one ormore alcohol solvents. For certain overcoat compositions, an alcohol mayprovide enhanced solubility with respect to the solid components.Suitable alcohol solvents include, for example: straight, branched orcyclic C4-C8 monohydric alcohol such as 1-butanol, 2-butanol, isobutylalcohol, tert-butyl alcohol, 3-methyl-1-butanol, 1-pentanol, 2-pentanol,4-methyl-2-pentanol, 1-hexanol, 1-heptanol, 2-hexanol, 2-heptanol,3-hexanol, 3-heptanal, 1-octanol, octanol, 3-octanol, 4-octanol,2,2,3,3,4,4-hexafluoro-1-butanol, 2,2,3,3,4,4,5,5-octafluoro-1-pentanoland 2,2,3,3,4,4,5,5,6,6-decafluoro-1-hexanol; and C5-C9 fluorinateddiols such as 2,2,3,3,4,4-hexafluoro-1,5-pentanediol,2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol and2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoro-1,8-octanediol. The alcohol solventis preferably a C4-C8 monohydric alcohol, with 4-methyl-2-pentanol beingpreferred. The one or more alcohol solvents if used in the overcoatcompositions are typically present in a combined amount of less than 50wt %, more typically in an amount of from 2 to 30 wt %, based on thetotal solvent of the overcoat composition.

The solvent system can include one or more additional solvents chosen,for example, from one or more of ketones such as 2,5-dimethyl-4-hexanoneand 2,6-dimethyl-4-heptanone; aliphatic hydrocarbons such as n-heptane,2-methylheptane, 3-methylheptane, 3,3-dimethylhexane,2,3,4-trimethylpentane, n-octane, n-nonane, and n-decane; fluorinatedaliphatic hydrocarbons such as perfluoroheptane; and diethers such asdipropylene glycol monomethyl ether. Such additional solvents, if used,are typically present in a combined amount of from 1 to 20 wt % based onthe solvent system.

A particularly preferred solvent system includes the one or more estersolvents as described above in a combined amount of from 2 to 30 wt %and one or more ether solvents in a combined amount of from 70 to 98 wt%, based on the total solvent of the overcoat composition.

The one or more solvents are typically present in the overcoatcomposition in a combined amount of from 90 to 99 wt %, preferably from95 to 99 wt %, based on the overcoat composition.

The overcoat compositions can optionally include an acid or an acidgenerator such as a thermal acid generator (TAG), or can be free of suchcomponents. In the case of a photoresist based on deprotection reaction,the acid or generated acid with heat can cause cleavage of the bonds ofacid labile groups in a surface region of the photoresist pattern,causing increased solubility of the photoresist polymer in a developingsolution to be applied. Inclusion of an acid or acid generator in theovercoat compositions can thereby allow for increased amount of resistremoval from the surface of the resist pattern.

The acid may take the form of one or more acid groups (e.g., carboxylicacid or sulfonic acid group) on the matrix polymer. Acidgroup-containing units on the polymer can be present, for example, in anamount of 30 mol % or less, based on the matrix polymer.

Additionally or alternatively, the acid can be in non-polymeric form.Preferable non-polymeric acids are organic acids including bothnon-aromatic acids and aromatic acids optionally having fluorinesubstitution. Suitable organic acids include, for example: carboxylicacids and polycarboxylic acids such as alkanoic acids, including formicacid, acetic acid, propionic acid, butyric acid, dichloroacetic acid,trichloroacetic acid, perfluoroacetic acid, perfluorooctanoic acid,oxalic acid malonic acid and succinic acid; hydroxyalkanoic acids, suchas citric acid; aromatic carboxylic acids such as benzoic acid,fluorobenzoic acid, hydroxybenzoic acid and naphthoic acid; organicphosphorus acids such as dimethylphosphoric acid and dimethylphosphinicacid; and sulfonic acids such as optionally fluorinated alkylsulfonicacids including methanesulfonic acid, trifluoromethanesulfonic acid,ethanesulfonic acid, 1-butanesulfonic acid, 1-perfluorobutanesulfonicacid, 1,1,2,2-tetrafluorobutane-1-sulfonic acid,1,1,2,2-tetrafluoro-4-hydroxybutane-1-sulfonic acid, 1-pentanesulfonicacid, 1-hexanesulfonic acid, 1-heptanesulfonic acid, and the following:

The non-polymeric acid when used on the overcoat compositions istypically present in an amount of from about 0.01 to 20 wt % based ontotal solids of the overcoat composition.

Suitable thermal acid generators include those capable of generating thenon-polymeric acids described above. The thermal acid generator can benon-ionic or ionic. Preferably, the TAG is ionic with a reaction schemefor generation of a sulfonic acid as shown below:

wherein RSO₃ ⁻ is the TAG anion and X⁺ is the TAG cation, preferably anorganic cation. The cation can be a nitrogen-containing cation of thegeneral formula (1):

(BH)⁺  (I)

Which is the monoprotonated form of a nitrogen-containing base B.Suitable nitrogen-containing bases B include, for example: optionallysubstituted amines such as ammonia, difluoromethylammonia, C1-20 alkylamines, and C3-30 aryl amines, for example, nitrogen-containingheteroaromatic bases such as pyridine or substituted pyridine (e.g.,3-fluoropyridine), pyrimidine and pyrazine; nitrogen-containingheterocyclic groups, for example, oxazole, oxazoline, or thiazoline. Theforegoing nitrogen-containing bases B can be optionally substituted, forexample, with one or more group chosen from alkyl, aryl, halogen atom(preferably fluorine), cyano, nitro and alkoxy. Of these, base B ispreferably a heteroaromatic base.

Base B typically has a pKa from 0 to 5.0, or between 0 and 4.0, orbetween 0 and 3.0, or between 1.0 and 3.0. As used herein, the term“pK_(a)” is used in accordance with its art-recognized meaning, that is,pK_(a) is the negative log (to the base 10) of the dissociation constantof the conjugate acid (BH)⁺ of the basic moiety (B) in aqueous solutionat about room temperature. In certain embodiments, base B has a boilingpoint less than about 170° C., or less than about 160° C., 150° C., 140°C., 130° C., 120° C., 110° C., 100° C. or 90° C.

Exemplary suitable nitrogen-containing cations (BH)⁺ include NH₄ ⁺,CF₂HNH₂ ⁺, CF₃CH₂NH₃ ⁺, (CH₃)₃NH⁺, (C₂H₅)₃NH⁺, (CH₃)₂(C₂H₅)NH⁺ and thefollowing:

in which Y is alkyl, preferably, methyl or ethyl.

Other suitable cations include onium cations. Suitable onium cationsinclude, for example, sulfonium and iodonium cations, for example, thoseof the following general formula (II):

wherein X is S or I, wherein when X is I then a is 2, and when X is Sthen a is 3; R₃ is independently chosen from organic groups such asoptionally substituted C₁₋₃₀ alkyl, polycyclic or monocyclic C₃₋₃₀cycloalkyl, polycyclic or monocyclic C₆₋₃₀ aryl, or a combinationthereof, wherein when X is S, two of the R₃ groups together optionallyform a ring.

Exemplary suitable sulfonium and iodonium cations include the following:

When present the acid generator is typically present in the compositionin an amount of from about 0.01 to 20 wt % based on the total solids ofthe overcoat composition.

The overcoat composition can further include a surfactant. Typicalsurfactants include those which exhibit an amphiphilic nature, meaningthat they can be both hydrophilic and hydrophobic at the same time.Amphiphilic surfactants possess a hydrophilic head group or groups,which have a strong affinity for water and a long hydrophobic tail,which is organophilic and repels water. Suitable surfactants can beionic (i.e., anionic, cationic) or nonionic. Further examples ofsurfactants include silicone surfactants, poly(alkylene oxide)surfactants, and fluorochemical surfactants. Suitable non-ionicsurfactants include, but are not limited to, octyl and nonyl phenolethoxylates such as TRITON® X-114, X-100, X-45, X-15 and branchedsecondary alcohol ethoxylates such as TERGITOL™ TMN-6 (The Dow ChemicalCompany, Midland, Mich. USA). Still further exemplary surfactantsinclude alcohol (primary and secondary) ethoxylates, amine ethoxylates,glucosides, glucamine, polyethylene glycols, polyethyleneglycol-co-propylene glycol), or other surfactants disclosed inMcCutcheon's Emulsifiers and Detergents, North American Edition for theYear 2000 published by Manufacturers Confectioners Publishing Co. ofGlen Rock, N.J. Nonionic surfactants that are acetylenic diolderivatives also can be suitable. Such surfactants are commerciallyavailable from Air Products and Chemicals, Inc. of Allentown, Pa. andsold under the trade names of SURFYNOL® and DYNOL®. Additional suitablesurfactants include other polymeric compounds such as the tri-blockEO-PO-EO co-polymers PLURONIC® 25R2, L121, L123, L31, L81, L101 and P123(BASF, Inc.). Such surfactant and other optional additives if used aretypically present in the composition in minor amounts such as from 0.01to 10 wt % based on total solids of the overcoat composition. Theovercoat compositions are preferably free of cross-linking agents assuch materials can result in a dimensional increase of the photoresistpattern.

The overcoat compositions can be prepared following known procedures.For example, the compositions can be prepared by dissolving solidcomponents of the composition in the solvent components. The desiredtotal solids content of the compositions will depend on factors such asthe desired final layer thickness. Preferably, the solids content of theovercoat compositions is from 1 to 10 wt %, more preferably from 1 to 5wt %, based on the total weight of the composition.

Photoresist Compositions

Photoresist compositions useful in the pattern formation methods aretypically chemically amplified positive photoresist compositionssuitable for KrF and/or EUV exposure. Preferred photoresist compositionsinclude a vinyl aromatic-based matrix polymer such as apolyhydroxystyrene-based polymer. Preferred matrix polymers comprise arepeat unit of the following formula (III):

wherein: R₄ is hydrogen or methyl; R₅ is one or more groups chosen fromhydroxyl, C1-C8 alkoxy, C5-C12 aryloxy, C2-C10 alkoxycarbonyloxy, C1-C4alkyl, C5-C15 aryl and C6-C20 aralkyl, wherein one or more carbonhydrogens are optionally substituted with a halogen atom; b is aninteger of from 1 to 5; wherein at least one R₅ is independently chosenfrom hydroxyl, C1-C8 alkoxy, C5-C12 aryloxy and C2-C10alkoxycarbonyloxy.

The matrix polymer typically also includes repeat units having an acidlabile leaving group, for example units of general formula (IV) in whichthe hydroxyl moiety of a carboxyl group is substituted with an acidlabile group:

wherein: R₆ represents hydrogen, C1-C4 alkyl or C1-C4 fluoroalkyl; R₇represents an acid labile group; Y₁ is a single bond or a C1-C12divalent linking group that optionally is halogenated or contains one ormore of ester, ether or ketone groups.

Suitable acid labile groups for R₇ include, but are not limited to thefollowing:

The photoresist matrix polymer may further comprise recurring units ofan onium salt photoacid generator. Suitable such units include, forexample, those of the general formulae (V) and (VI):

In formulae (V) and (VI), R₈ represents hydrogen, C1-C4 alkyl or C1-C4fluoroalkyl; R₉, R₁₀ and R₁₁ each independently represents a straight,branched or cyclic C1-C12 alkyl group which may contain a carbonyl,ester or ether substituent, or a C6-C12 amyl group, a C7-C20 aralkylgroup or a thiophenyl group; R₉ and R₁₀ may connect to form singlecyclic or fused cyclic structures; X₂ and X₃ each independentlyrepresent a single bond, a C1-C12 divalent linking group that optionallycontains one or more of a halogen atom or a group chosen from ester,ether, ketone and aromatic; Y₂ represents a single bond, optionallyfluorinated methylene or ethylene, optionally fluorinated phenylene,—OR₁₂—, or —C(O)Y₃R₁₂—, wherein Y₃ is oxygen or NH, and R₁₂ is a groupchosen from straight, branched or cyclic C1-C6 alkylene, phenylene,fluorophenylene, trifluoromethyl-substituted phenylene or alkenylene,which may contain a carbonyl, ester, ether or hydroxyl substituent; Zrepresents S or I; n is an integer of 0 or 1, provided that when Z is S,n is 1 and when Z is I, n is 0.

Suitable exemplary sulfonium and iodonium PAG monomers for use in thephotoresist matrix polymer include the following:

where R₈ represents hydrogen, C1-C4 alkyl or C1-C4 fluoroalkyl.

The matrix polymer may be synthesized using well known free radicalpolymerization techniques known in the art. For example, the polymer maybe synthesized by dissolving the monomers in an organic solvent, addinga radical polymerization initiator thereto, and effecting heatpolymerization to form the polymer. Suitable organic solvents that canbe used for the polymerization include, for example, toluene, benzene,tetrahydrofuran, diethyl ether and dioxane. Suitable polymerizationinitiators include, for example, 2,2′-azobisisobutyronitrile (AIBN),2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl2,2-azobis(2-methylpropionate), benzoyl peroxide and lauroyl peroxide.

When copolymerizing certain hydroxy aromatic monomers such ashydroxystyrene or hydroxyvinylnaphthalene, an alternative polymerizationmethod may be desired due to the relative instability of such monomers.The polymerization may, for example, take place using protected phenolichydroxyl groups and subsequently deprotecting the polymer. For example,acetoxystyrene or acetoxyvinylnaphthalene monomers can be used in thepolymerization instead of hydroxystyrene or hydroxyvinylnaphthalene.After polymerization, the acetoxy group can then be deprotected by acidor alkaline hydrolysis to convert those units to hydroxystyrene orhydroxyvinylnaphthalene units.

Typically, the copolymer will have a Mw of from 1,000 to 50,000, moretypically from 10,000 to 30,000 with a typical polydispersity index(PDI=Mw/Mn) of 3 or less, preferably 2 or less, as measured by GPCversus polystyrene standards.

The preferred resist compositions further comprise an additive photoacidgenerator that does not form part of the matrix polymer. The additivePAG can be ionic or non-ionic. Suitable additive PAGs are described, forexample, in U.S. Pat. No. 7,704,668B1, U.S. Pat. No. 9,182,669B2 andU.S. Pat. No. 6,740,467B2, and also include the following exemplarycompounds:

The photoresist compositions can include one or more other optionalmaterials, for example, added bases, surfactants, actinic and contrastdyes, anti-striation agents, plasticizers, speed enhancers andsensitizers. Such optional additives typically will be present in minorconcentration in the photoresist compositions except for fillers anddyes which may be present in relatively large concentrations such as,e.g., in amounts of from 5 to 30 percent by weight of the total weightof a resist's dry components.

The photoresist compositions can be prepared following known procedures.For example, the compositions can be prepared by dissolving solidcomponents of the composition in the solvent components. The desiredtotal solids content of the compositions will depend on factors such asthe desired final layer thickness. Typically, the solids content of thephotoresist compositions is from 5 to 35 wt % based on the total weightof the composition.

Pattern Formation Methods

Processes in accordance with the invention will now be described withreference to FIG. 1A-H, which illustrates an exemplary process flow fora pattern formation method in accordance with the invention. While theillustrated process flow describes a patterning process in which asingle resist mask is used to transfer the photoresist pattern to theunderlying substrate, it should be clear that the method can be used inother lithographic processes, for example, in double patterningprocesses such as litho-litho-etch (LLE), litho-etch-litho-etch (LELE)or self-aligned double patterning (SADP), as an ion implantation mask,or any other lithographic process where such photoresist patterntreatment would be beneficial. Also, while

FIG. 1A depicts in cross-section a substrate 100 which may includevarious layers and features. The substrate can be of a material such asa semiconductor, such as silicon or a compound semiconductor (e.g.,III-V or II-VI), glass, quartz, ceramic, copper and the like. Typically,the substrate is a semiconductor wafer, such as single crystal siliconor compound semiconductor water, and may have one or more layers andpatterned features formed on a surface thereof. One or more layers to bepatterned 102 may be provided over the substrate 100. Optionally, theunderlying base substrate material itself may be patterned, for example,when it is desired to form trenches in the substrate material. In thecase of patterning the base substrate material itself, the pattern shallbe considered to be formed in a layer of the substrate.

The layers may include, for example, one or more conductive layers suchas layers of aluminum, copper, molybdenum, tantalum, titanium, tungsten,alloys, nitrides or silicides of such metals, doped amorphous silicon ordoped polysilicon, one or more dielectric layers such as layers ofsilicon oxide, silicon nitride, silicon oxynitride, or metal oxides,semiconductor layers, such as single-crystal silicon, and combinationsthereof. The layers to be etched can be formed by various techniques,for example, chemical vapor deposition (CVD) such as plasma-enhancedCVD, low-pressure CVD or epitaxial growth, physical vapor deposition(PVD) such as sputtering or evaporation, or electroplating. Theparticular thickness of the one or more layers to be etched 102 willvary depending on the materials and particular devices being formed.

Depending on the particular layers to be etched, film thicknesses andphotolithographic materials and process to be used, it may be desired todispose over the layers 102 a hard mask layer 103 and/or a bottomantireflective coating (BARC) 104 over which a photoresist layer 106 isto be coated. Use of a hard mask layer may be desired, for example, withvery thin resist layers, where the layers to be etched require asignificant etching depth, and/or where the particular etchant has poorresist selectivity. Where a hard mask layer is used, the resist patternsto be formed can be transferred to the hard mask layer 103 which, inturn, can be used as a mask for etching the underlying layers 102.Suitable hard mask materials and formation methods are known in the art.Typical materials include, for example, tungsten, titanium, titaniumnitride, titanium oxide, zirconium oxide, aluminum oxide, aluminumoxynitride, hafnium oxide, amorphous carbon, silicon oxynitride andsilicon nitride. The hard mask layer can include a single layer or aplurality of layers of different materials. The hard mask layer can beformed, for example, by chemical or physical vapor depositiontechniques.

A bottom antireflective coating may be desirable where the substrateand/or underlying layers would otherwise reflect a significant amount ofincident radiation during photoresist exposure such that the quality ofthe formed pattern would be adversely affected. Such coatings canimprove depth-of-focus, exposure latitude, linewidth uniformity and CDcontrol. Antireflective coatings are typically used where the resist isexposed to deep ultraviolet light (300 nm or less), for example, KrF(248 nm). ArF (193 nm) and EUV (13.5 nm). The antireflective coating cancomprise a single layer or a plurality of different layers. Suitableantireflective materials and methods of formation are known in the art.Antireflective materials are commercially available, for example, thosesold under the AR™ trademark by Rohm and Haas Electronic Materials LLC(Marlborough, Mass. USA), such as AR™ 40A and AR™ 124 antireflectantmaterials.

A photoresist layer 106 as described herein is formed from a photoresistmaterial, typically a chemically amplified photosensitive composition,comprising a matrix polymer having acid labile groups. The photoresistlayer is disposed on the substrate over the antireflective layer 104 (ifpresent). The photoresist composition can be applied to the substrate byspin-coating, dipping, roller-coating or other conventional coatingtechnique. Of these, spin-coating is typical. For spin-coating, thesolids content of the coating solution can be adjusted to provide adesired film thickness based upon the specific coating equipmentutilized, the viscosity of the solution, the speed of the coating tooland the amount of time allowed for spinning. A typical thickness for thephotoresist layer 106 is from about 500 to 3000 Å.

The photoresist layer 106 can next be softbaked to minimize the solventcontent in the layer, thereby forming a tack-free coating and improvingadhesion of the layer to the substrate. The softbake can be conducted ona hotplate or in an oven, with a hotplate being typical. The softbaketemperature and time will depend, for example, on the particularmaterial of the photoresist and thickness. Typical softbakes areconducted at a temperature of from about 90 to 150° C. and a time offrom about 30 to 90 seconds.

The photoresist layer 106 is next exposed to activating radiation 108through a photomask 110 to create a difference in solubility betweenexposed and unexposed regions. References herein to exposing aphotoresist composition to radiation that is activating for thecomposition indicates that the radiation is capable of forming a latentimage in the photoresist composition. The photomask has opticallytransparent and optically opaque regions corresponding to regions of theresist layer to be exposed and unexposed, respectively, by theactivating radiation. The exposure wavelength is typically sub-400 nm,sub-300 nm, such as 248 nm or an EUV wavelength (e.g., 13.5 nm), with248 nm and EUV wavelengths being preferred. The exposure energy istypically from about 10 to 80 mJ/cm², dependent upon the exposure tooland the components of the photosensitive composition.

Following exposure of the photoresist layer 106, a post-exposure bake(PEB) is typically performed. The PEB can be conducted, for example, ona hotplate or in an oven. Conditions for the PEB will depend, forexample, on the particular photoresist composition and layer thickness.The PEB is typically conducted at a temperature of from about 80 to 150°C., and a time of from about 30 to 90 seconds. A latent image defined bythe boundary between polarity-switched and unswitched regions(corresponding to exposed and unexposed regions, respectively) isthereby formed.

The photoresist layer 106 is next developed to remove exposed regions ofthe layer, leaving unexposed regions forming a resist pattern 106′having a plurality of features as shown in FIG. 19. The features are notlimited and can include, for example, a plurality of lines and/orcontact hole patterns which allow for the formation of such patterns inthe underlying layers to be patterned. The formed patterns have aninitial dimension shown as L₁, a linewidth in the case of line patternsor post diameter for post patterns.

A layer 112 of a photoresist pattern overcoat composition as describedherein is formed over the photoresist pattern 106′ as shown in FIG. 1C.The overcoat composition is typically applied to the substrate byspin-coating. The solids content of the coating solution can be adjustedto provide a desired film thickness based upon the specific coatingequipment utilized, the viscosity of the solution, the speed of thecoating tool and the amount of time allowed for spinning. A typicalthickness for the pattern overcoat layer 112 is from 200 to 1500 Å,typically measured on an unpatterned substrate.

As shown in FIG. 1D, the substrate is next baked to remove solvent inthe overcoat composition layer. The bake can also activate an optionallyincluded thermal acid generator and allow the generated acid, or anoptional free acid, to diffuse into the surface of the resist pattern106′ to cause a polarity-changing reaction in the resist pattern surfaceregion 114. The bake can be conducted with a hotplate or oven, with ahotplate being typical. Suitable bake temperatures are greater than 50°C., for example, greater than 70° C., greater than 90° C., greater than120° C. or greater than 150° C., with a temperature of from 70 to 160°C. and a time of from about 30 to 90 seconds being typical. While asingle baking step is typical, multiple-step baking can be used and maybe useful for resist profile adjustment.

The photoresist pattern is next contacted with a rinsing agent,typically a developing solution, to remove the residual overcoatcomposition layer 112 and typically also the surface region 114 of thephotoresist pattern, with the resulting pattern 106″ being shown in FIG.1E. The rinsing agent is typically an aqueous alkaline developer, forexample, a quaternary ammonium hydroxide solution, for example, atetra-alkyl ammonium hydroxide solutions such as 0.26 Normality (N)(2.38 wt %) tetramethylammonium hydroxide (TMAH). The rinsing agent canfurther be or comprise water. The resulting structure is shown in FIG.1E. The resist pattern after overcoat treatment has a dimension (L₂)that is smaller as compared with the feature size prior to overcoattreatment.

Using the resist pattern 106″ as an etch mask, the BARC layer 104 isselectively etched to form BARC patterns 104′, exposing the underlyinghardmask layer 103, as shown in FIG. 1F. The hardmask layer is nextselectively etched, again using the resist pattern as an etch mask,resulting in patterned BARC and hardmask layer 103′, as shown in FIG.1G. Suitable etching techniques and chemistries for etching the BARClayer and hardmask layer are known in the art and will depend, forexample, on the particular materials of these layers. Dry-etchingprocesses such as reactive ion etching are typical. The resist pattern106″ and patterned BARC layer 104′ are next removed from the substrateusing known techniques, for example, oxygen plasma aching. Using thehardmask pattern 103′ as an etch mask, the one or more layers 102 arethen selectively etched. Suitable etching techniques and chemistries foretching the underlying layers 102 are known in the art, with dry-etchingprocesses such as reactive ion etching being typical. The patternedhardmask layer 103′ can next be removed from the substrate surface usingknown techniques, for example, a dry-etching process such as reactiveion etching or a wet strip. The resulting structure is a pattern ofetched features 102′ as illustrated in FIG. 1H. In an alternativeexemplary method, it may be desirable to pattern the layer 102 directlyusing the photoresist pattern 106″ without the use of a hardmask layer103. Whether direct patterning with the resist patterns can be employedwill depend on factors such as the materials involved, resistselectivity, resist pattern thickness and pattern dimensions.

The following non-limiting examples are illustrative of the invention.

EXAMPLES Polymer Synthesis

The following monomers were used to synthesize polymers according to theprocedures described below:

Polymer P1 Synthesis

A monomer feed solution was prepared by combining 23.77 g propyleneglycol monomethyl ether (PGME) and 22.80 g monomer M1 in a container andagitating the mixture to dissolve the monomer. 1.92 g monomer M3 wasdissolved in 1.92 g of distilled water in a container and the mixturewas agitated to dissolve the monomer. This monomer (M3) solution wasadded to and mixed with the reaction mixture. An initiator feed solutionwas prepared by combining 0.39 g Vazo 67 free radical initiator (E. I.du Pont de Nemours and Company) and 3.53 g of PGME in a container andagitating the mixture to dissolve the initiator. 27.11 g of PGME wasintroduced into a reaction vessel and the vessel was purged withnitrogen gas for 30 minutes. The reaction vessel was next heated to 90°C. with agitation. Introduction of the monomer feed solution andinitiator feed solution into the reaction vessel was simultaneouslystarted. The monomer feed solution was fed over a period of 2 hours andthe initiator feed solution was fed over a period of 3 hours. Thereaction vessel was maintained at 90° C. for an additional 7 hours withagitation, and was then allowed to cool to room temperature. Thereaction mixture was precipitated in water (1000 mL) to yield polymer P1as a white solid which was further dried under vacuum at 40° C. PolymerP1 was thereby formed. Weight average molecular weight (Mw) andpolydispersity (PDI=Mw/Mn) were determined by polystyrene equivalentvalue as measured by gel permeation chromatography (GPC). [Mw=10735Daltons, PDI=1.81].

Polymer P2 Synthesis

A monomer teed solution was prepared by combining 10.88 g PGME and 30.40g monomer M2 in a container and agitating the mixture to dissolve themonomer. 2.56 g monomer M3 was dissolved in 2.56 a of distilled water ina container and the mixture was agitated to dissolve the monomer. Thismonomer (M3) solution was added to and mixed with the reaction mixture.An initiator feed solution was prepared by combining 1.23 g Vazo 67 freeradical initiator (E. I. du Pont de Nemours and Company) and 11.05 g ofPGME in a container and agitating the mixture to dissolve the initiator.23.24 g of PGME was introduced into a reaction vessel and the vessel waspurged with nitrogen gas for 30 minutes. The reaction vessel was nextheated to 90° C. with agitation. Introduction of the monomer feedsolution and initiator feed solution into the reaction vessel wassimultaneously started. The monomer feed solution was fed over a periodof 2 hours and the initiator feed solution was fed over a period of 3hours. The reaction vessel was maintained at 90° C. for an additional 7hours with agitation, and was then allowed to cool to room temperature.The reaction mixture was precipitated in water (1000 mL) to yieldpolymer P2 as a white solid which was further dried wider vacuum at 40°C. Polymer P2 was thereby formed. Weight average molecular weight (Mw)and polydispersity (PDI=Mw/Mn) were determined by polystyrene equivalentvalue as measured by gel permeation chromatography (GPC). [Mw=17374Daltons, PDI=2.42].

Polymer P3 Synthesis

A monomer feed solution was prepared by mixing 23.67 g4-methyl-2-pentanol (MIBC), 15.80 g Monomer M2 and 1.76 g Monomer M4 ina container and agitating the mixture to dissolve the two monomers. Aninitiator feed solution was prepared by combining 0.53 g Vazo-67 freeradical initiator (E. I. du Pont de Nemours and Company) and 17.03 g ofMIBC in a container and agitating the mixture to dissolve the initiator.41.23 g of MIBC was introduced into a reaction vessel and the vessel waspurged with nitrogen gas for 30 minutes. The reaction vessel was nextheated to 90° C. with agitation. Introduction of the monomer feedsolution and initiator feed solution into the reaction vessel wassimultaneously started. The monomer feed solution was fed over a periodof 2 hours and the initiator feed solution was fed over a period of 3hours. The reaction vessel was maintained at 90° C. for an additional 7hours with agitation, and was then allowed to cool to room temperature.The resulting polymer solution was precipitated in heptane (2000 mL) toyield polymer P3 as a white solid which was further dried under vacuumat 40° C. Polymer P3 was thereby formed. Weight average molecular weight(Mw) and polydispersity (PDI=Mw/Mn) were determined by polystyreneequivalent value as measured by gel permeation chromatography (GPC).[Mw=12316 Daltons, PDI=2.28].

Polymer P4 Synthesis

A monomer feed solution was prepared by mixing 9.85 g MIBC and 45.00 gMonomer M2 in a container. An initiator feed solution was prepared bycombining 1.76 g Vazo-67 free radical initiator (E. I. du Pont deNemours and Company) and 15.88 g of MIBC in a container and agitatingthe mixture to dissolve the initiator. 27.50 g of MIBC was introducedinto a reaction vessel and the vessel was purged with nitrogen gas for30 minutes. The reaction vessel was next heated to 90° C. withagitation. Introduction of the monomer feed solution and initiator feedsolution into the reaction vessel was simultaneously started. Themonomer feed solution was fed over a period of 2 hours and the initiatorfeed solution was fed over a period of 3 hours. The reaction vessel wasmaintained at 90° C. for an additional 7 hours with agitation, and wasthen allowed to cool to room temperature. The resulting polymer solutionwas precipitated in heptane (2000 mL) to yield polymer P4 as a whitesolid which was further dried under vacuum at 40° C. Polymer P4 wasthereby formed. Weight average molecular weight (Mw) and polydispersity(PDI=Mw/Mn) were determined by polystyrene equivalent value as measuredby gel permeation chromatography (GPC). [Mw=15966 Daltons, PDI=1.93].

Polymer P5 Synthesis

A monomer feed solution was prepared by mixing 13.91 g MIBC and 36.00 gMonomer M1 in a container. An initiator feed solution was prepared bycombining 0.81 g Vazo-67 free radical initiator (E. I. du Pont deNemours and Company) and 7.2.8 g of MIBC in a container and agitatingthe mixture to dissolve the initiator. 22.00 g of MIBC was introducedinto a reaction vessel and the vessel was purged with nitrogen gas for30 minutes. The reaction vessel was next heated to 90° C. withagitation. Introduction of the monomer feed solution and initiator feedsolution into the reaction vessel was simultaneously started. Themonomer feed solution was fed over a period of 2 hours and the initiatorteed solution was fed over a period of 3 hours. The reaction vessel wasmaintained at 90° C. for an additional 7 hours with agitation, and wasthen allowed to cool to room temperature. The resulting polymer solutionwas precipitated in heptane (2000 mL) to yield polymer P5 as a whitesolid which was further dried under vacuum at 40° C. Polymer P5 wasthereby formed. Weight average molecular weight (Mw) and polydispersity(PDI=Mw/Mn) were determined by polystyrene equivalent value as measuredby gel permeation chromatography (GPC). [Mw=19515 Daltons, PDI=1.90].

Preparation of Pattern Overcoat Compositions (PUC)

Photoresist pattern overcoat compositions were prepared by dissolvingrespective polymers in solvents using the materials and amounts setforth in Table 1. The resulting mixtures were shaken on a mechanicalshaker for 3 to 24 hours and then filtered through a Teflon filterhaving a 0.2 micron pore size.

TABLE 1 Pattern Overcoat Polymer Solvent (wt %) Example Composition (wt%) S1 S2 S3 S4 Ex. 1 POC-1 P1 (5) 9.5 85.5 Ex. 2 POC-2 P2 (5) 9.5 85.5Ex. 3 POC-3 P3 (5) 9.5 85.5 Ex. 4 POC-4 P1 (5) 28.5 66.5 Ex. 5 POC-5 P2(5) 28.5 66.5 Ex. 6 POC-6 P3 (5) 28.5 66.5 Ex. 7 POC-7 P1 (5) 95 Ex. 8POC-8 P2 (5) 95 Ex. 9 POC-9 P3 (5) 95 Ex. 10 POC-10 P1 (5) 9.5 80.8 4.7Ex. 11 POC-11 P2 (5) 9.5 80.8 4.7 Ex. 12 POC-12 P3 (5) 9.5 80.8 4.7 Ex.13 POC-13 P2 (3.3) 82.2 4.8 9.7 Ex. 14 POC-14 P4 (3.3) 19.3 77.4 Ex. 15POC-15 P4 (2.9) 9.7 87.4 Comp. 1 POC-16 P1 (5) 95 Comp. 2 POC-17 P2 (5)95 Comp. 3 POC-18 P3 (5) 95 Comp. 4 POC-19 P4 (3.3) 4.8 91.9 Comp. 5POC-20 P4 (3.3) 96.7 Comp. 6 POC-21 P4 (2.9) 85.4 8.7 2.9 Comp. 7 POC-22P5 (3.3) 96.7 S1 = Isoamyl isobutyrate; S2 = Isoamyl ether; S3 = Methylisobutyl carbinol; S4 = Dipropyleneglycol monomethyl ether; all amountsprovided as weight percent (wt %) based on total pattern overcoatcomposition.

Solubility Test

The polymers and solvents in the amounts shown in Table 2 were mixed andhand-shaken in a 20 mL glass container for 1 minute. Turbidity was thenmeasured with an Orbeco-Hellige 965-10 Turbidimeter. The results areshown in Table 2, wherein “O” indicates a good solubility with aturbidity of less than or equal to 1; and “X” indicates poor solubilitywith a turbidity of greater than 1.

TABLE 2 Solvent (wt %) Example Polymer (wt %) S1 S2 S3 Solubility Ex. 16P1 (5) 9.5 85.5 ◯ Ex. 17 P2 (5) 9.5 85.5 ◯ Ex. 18 P3 (5) 9.5 85.5 ◯ Ex.19 P1 (5) 28.5 66.5 ◯ Ex. 20 P2 (5) 28.5 66.5 ◯ Ex. 21 P3 (5) 28.5 66.5◯ Ex. 22 P1 (5) 95 ◯ Ex. 23 P2 (5) 95 ◯ Ex. 24 P3 (5) 95 ◯ Ex. 25 P1 (5)9.5 80.8 4.7 ◯ Ex. 26 P2 (5) 9.5 80.8 4.7 ◯ Ex. 27 P3 (5) 9.5 80.8 4.7 ◯Comp. 8 P1 (5) 95 X Comp. 9 P2 (5) 95 X Comp. 10 P3 (5) 95 X S1 =Isoamyl isobulyrate; S2 = Isoamyl ether; S3 = Methyl isobulyl catbinol;all amounts provided as weight percent (wt %) based on total patternovercoat composition.

Photoresist Pattern Overcoat Composition Evaluation Lithography and CDEvaluation

200 mm silicon wafers were coated with AR™3-600 organic bottomanti-reflective coating material (Dow Electronic Materials) to athickness of 600 Å. The wafers were baked at 205° C. for 60 seconds.UV™1610 polyhydroxystyrene-based photoresist (Dow Electronic Materials)was coated over the wafers using a TEL ACTS clean track. The waters weresoftbaked at 120° C. for 60 seconds to give target thickness of 862 Å.The coated wafers were exposed to KrF (248 nm) radiation on a CANONFPA-5000 ES4 DUV scanner with NA=0.68, conventional illumination (Sigma,0.75) using a binary reticle with 175 nm diameter 1:1 dense contact holepatterns. The wafers were post-exposure baked at 130° C. for 60 secondsand developed using 0.26 N aqueous TMAH solution for 50 seconds. CDs ofthe resist patterns of one of the wafers were measured using a HitachiHigh Technologies Co. CG4000 CD-SEM to obtain initial CD measurements.20 CD measurements were made on each of 5 SEM images across a single dieof the wafer. Wafers were next coated with a respective pattern overcoatcomposition as indicated in Table 3, baked at 100° C. for 60 seconds andrinsed using 0.26 N aqueous TMAH solution for 20 seconds. CDs of theresist patterns for the treated wafers were then measured as describedabove. The change in CD (ΔCD) for the treated patterns was calculatedaccording to the following equation:

ΔCD=CD_(f)−CD_(i)

wherein CD_(f) is the average CD measurement after overcoat treatment,and CD_(i) is the average CD measurement prior to overcoat treatment.The percentage change in local CD uniformity (ΔLCDU %) of the resistpatterns was calculated based on the standard deviation of the CDmeasurements according to the following equation:

ΔLCDU (%)=[(LCDU_(i)−LCDU_(f))/LCDU_(i)]·100

wherein LCDU_(i) is the standard deviation of the CD measurements priorto overcoat treatment and LCDU_(f) is the standard deviation of the CDmeasurements after overcoat treatment. The results are shown in Table 3.

TABLE 3 Pattern Overcoat Polymer Solvent (wt %) ΔCD ΔLCDU ExampleComposition (wt %) S1 S2 S3 (nm) (%) Ex. 28 POC-13 P2 (3.3) 82.2 9.7 4.87.5 34 Ex. 29 POC-14 P4 (3.3) 19.3 77.4 17.1 13 Comp. 11 POC-19 P4 (3.3)4.8 91.9 8.6 0 Comp. 12 POC-20 P4 (3.3) 96.7 7.5 5 S1 = Isoamylisobutyrate; S2 = Isoamyl ether; S3 = Methyl isobutyl carbinol; allamounts provided as weight percent (wt %) based on total patternovercoat composition.

Coating Defect Test

Pattern overcoat compositions were spin-coated at 1500 rpm on respective200 mm Si wafers. The coated wafers were baked at 80° C. for 60 seconds.The wafers were then inspected on a KLA-Tencor 2800/Surfscan SP2 wafersurface inspection system. The results are shown in Table 4 wherein eachTotal Defect result represents a separate wafer tested.

TABLE 4 Pattern Exam- Overcoat Polymer Solvent (wt %) Total pleComposition (wt %) S1 S2 S3 S4 Defects Ex. 30 POC-13 P2 (3.3) 82.2 9.74.8 71 55 Ex. 31 POC-15 P4 (2.9) 9.7 87.4 14 9 Comp. POC-19 P4 (3.3) 4.891.9 1020 5842 13 Comp. POC-20 P4 (3.3) 96.7 9853 9195 14 Comp. POC-21P4 (2.9) 85.4 8.7 2.9 >50k 15 Comp. POC-22 P5 (3.3) 96.7 1327 443 16 S1= Isoamyl isobutyrate; S2 = Isoamyl ether; S3 = Methyl isobutylcarbinol; S4 = Dipropyleneglycol monomethyl ether; all amounts providedas weight percent (wt %) based on total pattern overcoat composition.

1. A pattern formation method, comprising: (a) providing a semiconductorsubstrate; (b) forming a photoresist pattern over the semiconductorsubstrate, wherein the photoresist pattern is formed from a photoresistcomposition comprising: a first polymer comprising acid labile groups;and a photoacid generator; (c) coating a pattern overcoat compositionover the photoresist pattern, wherein the pattern overcoat compositioncomprises a second polymer and an organic solvent, wherein the organicsolvent comprises one or more ester solvents, wherein the ester solventis of the formula R₁—C(O)O—R₂, wherein R₁ is a C3-C6 alkyl group and R₂is a C5-C10 alkyl group; (d) baking the coated photoresist pattern; and(e) rinsing the coated photoresist pattern with a rinsing agent toremove the second polymer.
 2. The method of claim 1, wherein the firstpolymer comprises a repeat unit of the following formula (III):

wherein: R₄ is hydrogen or methyl; R₅ is one or more groups chosen fromhydroxyl, C1-C8 alkoxy, C5-C12 aryloxy, C2-C10 alkoxycarbonyloxy, C1-C4alkyl, C5-C15 aryl and C6-C20 aralkyl, wherein one or more carbonhydrogens are optionally substituted with a halogen atom; b is aninteger of from 1 to 5; wherein at least one R₅ is independently chosenfrom hydroxyl, C1-C8 alkoxy, C5-C12 aryloxy and C2-C10alkoxycarbonyloxy.
 3. The method of claim 1, wherein the ester solventis isoamyl isobutyrate.
 4. The method of claim 1, wherein the patternovercoat composition further comprises a second organic solvent that hasa lower boiling point than the ester solvent.
 5. The method of claim 4,wherein the second organic solvent is a monoether.
 6. The method ofclaim 1, wherein the pattern overcoat composition further comprises analcohol solvent.
 7. The method of claim 1, wherein the second polymercomprises a repeat unit comprising a —C(CF₃)₂OH group and/or a repeatunit comprising an acid group.
 8. The method of claim 1, wherein thepattern overcoat composition is free of non-polymeric acids andnon-polymeric acid generators.
 9. The method of claim 1, wherein therinsing agent is an aqueous tetramethylammonium hydroxide solution. 10.The method of claim 1, wherein forming the photoresist pattern comprisesexposing a layer formed from the photoresist composition to EUVradiation.
 11. A photoresist pattern overcoat composition, comprising: amatrix polymer comprising a repeat unit comprising a —C(CF₃)₂OH groupand/or a repeat unit comprising an acid group; and an organic solventcomprising one or more ester solvents, wherein the ester solvent is ofthe formula R₁—C(O)O—R₂, wherein R₁ is a C3-C6 alkyl group and R₂ is aC5-C10 alkyl group.
 12. The photoresist pattern overcoat composition ofclaim 11, wherein the ester solvent is isoamyl isobutyrate.
 13. Thephotoresist pattern overcoat composition of claim 11, further comprisinga second organic solvent that has a lower boiling point than the estersolvent.
 14. The photoresist pattern overcoat composition of claim 13,wherein the second organic solvent is a monoether.
 15. The photoresistpattern overcoat composition of claim 11, further comprising an alcoholsolvent.
 16. The photoresist pattern overcoat composition of claim 11,wherein the matrix polymer comprises a repeat unit comprising a—C(CF₃)₂OH group.
 17. The photoresist pattern overcoat composition ofclaim 11, wherein the matrix polymer comprises a repeat unit comprisingan acid group.
 18. The photoresist pattern overcoat composition of claim11, wherein the pattern overcoat composition is free of non-polymericacids and non-polymeric acid generators.
 19. A coated substrate,comprising: a semiconductor substrate; a photoresist pattern over thesubstrate; and a photoresist pattern overcoat composition of claim 11over and in contact with the photoresist pattern.
 20. The coatedsubstrate of claim 19, wherein the first polymer comprises a repeat unitof the following formula (III):

wherein: R₄ is hydrogen or methyl; R₅ is one or more groups chosen fromhydroxyl, C1-C8 alkoxy, C5-C12 aryloxy, C2-C10 alkoxycarbonyloxy, C1-C4alkyl, C5-C15 aryl and C6-C20 aralkyl, wherein one or more carbonhydrogens are optionally substituted with a halogen atom; b is aninteger of from 1 to 5; wherein at least one R₅ is independently chosenfrom hydroxyl, C1-C8 alkoxy, C5-C12 aryloxy and C2-C10alkoxycarbonyloxy.